# URGENT A level question

2 (a) Fig. 6.1
(b) A gas cylinder of internal volume 0.050 m3 contains compressed air at 21 °C and pressure
1.2 × 107 Pa. The molar mass of air is 0.029 kg mol–1.
(i) Calculate
1 the number of moles of air in the cylinder
number of moles = ........................250......................
2 the mass of air in the cylinder.
mass = .......................7.1......................... kg
[3]

(ii) An additional 1.5 m3 of air at 21 °C and at atmospheric pressure, 1.0 × 105 Pa, is pumped
into the cylinder. Calculate the new pressure of air in the cylinder, assuming no change in
temperature during the process.
pressure = ...................??.......................... Pa [4]

For the last part of the question, why does the mark scheme say not to include the added 1.5m^3 of volume in the calculation ie to say that P = nRT/V, where n is the moles before + new moles?
The second lot of air is at a lower pressure, in order to pump it into the cylinder containing the original air it'll need to be compressed to a higher pressure (and therefore lower volume)

You'll need to work with the mass or number of moles of the second lot of air which are going to remain constant as the second lot of air is compressed.
the volume doesnt matter as it is whats added to the initial container.(the containers arent connected, more gas is just added to the first one/) Ur given 1.5 m3 in order to calculate no.moles added
I see, i get that the dimensions of the cylinder are constant and therefore so is the volume. So does this mean the question is kind of poorly worded as all its saying is that there is additional gas instead of increase in volume?
(edited 2 months ago)
Original post by efsfsf\\eeeeeee
I see, i get that the dimensions of the cylinder are constant and therefore so is the volume. So does this mean the question is kind of poorly worded as all its saying is that there is additional gas instead of increase in volume?

i guess so. But it does say whats the pressure of the cylinder, suggewsting that you use the volume of the cylinder. i see how it might be confusing